The performance characteristics of polymers are determined not only by their composition but also by their molecular architecture. For copolymers, various properties such as melt viscosity, glass transition temperature, and modulus are often a function of the distribution of the different monomeric units along the polymeric chain. Conventional radical polymerization methods have limited utility in synthesizing polymers with precise architectural and structural characteristics.
Living controlled radical polymerization methods have been developed that allow the preparation of polymers with well-defined molecular weight, polydispersity, topology, composition, and microstructure. These methods are based on the use of special polymerization mediators, which temporarily and reversibly transform propagating radicals into dormant and/or stable species. The reversible transformations are typically either accomplished by reversible deactivation or by reversible chain transfer. Some of the methods that involve living controlled radical polymerization through reversible transformations include iniferter methods, nitroxide mediated polymerization (NMP) methods, atom transfer polymerization (ATRP) methods, and reversible addition-fragmentation (RAFT) methods.
The terms “iniferter” and “photoiniferters” refer to molecules that can act as an initiator, transfer agent, and terminator. Various iniferters were discussed in Otsu et al., Makromol. Chem., Rapid Commun., 3, 127-132 (1982). The compound p-xylene bis(N,N-diethyldithiocarbamate) (XDC) has been used to form various acrylic-based block copolymers such as those described in European Patent Applications 0286376 A2 (Otsu et al.) and 0349270 A2 (Mahfuza et al.).